Consequences of Tidal Dissipation in a Putative Venusian Ocean

J A Mattias Green,Rory Barnes,Michael J Way

doi:10.3847/2041-8213/ab133b

Abstract

Abstract The solar tide in an ancient Venusian ocean is simulated using a dedicated numerical tidal model. Simulations with varying ocean depth and rotational periods ranging from −243 to 64 sidereal Earth days are used to calculate the tidal dissipation rates and associated tidal torque. The results show that the tidal dissipation could have varied by more than 5 orders of magnitude, from 0.001 to 780 GW, depending on rotational period and ocean depth. The associated tidal torque is about 2 orders of magnitude below the present day Venusian atmospheric torque, and could change the Venusian daylength by up to 72 days per million years depending on rotation rate. Consequently, an ocean tide on ancient Venus could have had significant effects on the rotational history of the planet. These calculations have implications for the rotational periods of similarly close-in exoplanetary worlds and the location of the inner edge of the liquid water habitable zone.

Highlights

It has been argued that Venus may have had an ocean in its deep past (Hashimoto et al 2009; Hamano et al 2013; Shellnutt 2019), and it may have been habitable if its rotation rate was similar to today’s (Way et al 2016)
The horizontally integrated rate in the shallow simulation is a mere 0.15 GW (see Figure 2(a), which is discussed in detail below). This is a fraction of the dissipation of 600 GW from the solar tide in Earth’s oceans today
We show the results from the shallow prograde 8 day simulation in Figures 1(d) and (f), where a more energetic tide would be generated compared to a shallow present day Venusian ocean

Summary

Introduction

It has been argued that Venus may have had an ocean in its deep past (Hashimoto et al 2009; Hamano et al 2013; Shellnutt 2019), and it may have been habitable if its rotation rate was similar to today’s (Way et al 2016). We explore the subject of a Venusian ocean further by investigating tidally driven dissipation rates on ancient Venus to understand and constrain its history. This can help inform studies of ocean-bearing exoplanets where the rotation rate is critical to understanding climate dynamics (e.g., Yang et al 2014; Way et al 2018). Tides have been recognized as a potential driver for evolution and mass extinction events (Balbus 2014) These effects could be much stronger on other worlds (e.g., Barnes et al 2013), and a broad understanding of tidal dissipation over a range of planetary and orbital parameters could help our understanding of planetary evolution, as well as guide our search for life beyond Earth. It makes sense to start such simulations for a well-studied planet with an observed topography, rather than more speculative simulations for other exoplanets

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Conclusion